Suspensions of synthetic polymer fibrous products containing acrylamide polymer and method of making a paper web therefrom



United States Patent SUSPENSIGNS 0F SYNTHETIQ POLYMER FIBROUS PRODUCTS CONTAINING ACRYLAMIDE POLY- MER AND METHOD OF MAKING A PAPER WEB THEREFROM Thomas C. Spence, Yorktown, and Earl W. Malcolm, Wiliiamsburg, Va., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Deinware No Drawing. Continuation-impart of application Ser. No. 371,828, June 1, 1964. This application July 6, 1%5, Ser. No. 469,869

12 Claims. (Cl. 162-146) ABSTRACT OF THE DISCLOSURE Suspensions essentially adapted for providing more uniform webs are formed by adding 0.01 to 20 weight percent of a water soluble acrylamide polymer having a molect lar weight in excess of 750,000 and a percent hydrolysis not in excess of 40 percent to an aqueous suspension containing at least 50 weight percent of a non-cellulosic, fibrous synthetic polymer.

The present invention relates to aqueous suspensions of synthetic fibrous products and to a method for preparing wet-laid non-woven fibrous webs therefrom of improved uniformity. This application is a continuation-mpart of application Ser. No. 371,828 filed June 1, 1964, now abandoned.

The synthetic, hydrophobic textile fibers that were developed principally for textile end uses are now being employed in the development of numerous novelty and specialty papers plus other non-woven fibrous products not traditionally associated with the paper industry. Particular emphasis has been placed on the preparation of paper and paper-like webs from these polymeric fibrous products either to be ultimately used in unconverted form in a specialty paper end use or to be combined with other materials as in a laminate structure for its structural or esthetic characteristics. To this end, for obvious reasons including availability and economy, it has been advantageous to utilize conventional papermaking equipment and techniques which are well known.

The commonly employed paper manufacturing techniques are of two principal types, the Fourdrinier and the cylinder. Both involve a wet end, consisting of a wire section on which the paper sheet is formed from an aqueous suspension of the paper-making fibers and where the majority of the water is removed after the pulp has been sheeted out and a press section where the freshly formed sheet is condensed or pressed. The wet end is generally followed by a dry end wherein the wet paper web is calendered, dried-and polished.

, The sheet formation is generally considered to be the more critical part of the process since once the sheet is formed or cast the predominant properties of the sheet are fixed. It is apparent, therefore, that the manner in which the paper-forming fibers are deposited in the formation of the wet web strongly influences the properties of the finished paper or paper-like product. Thus, for example, the control of the web formation influences such properties in the final product as strength, appearance, the amount of directionalism in the tensile and tearing strengths, the amount of expansion and contraction of the sheet that will occur at different moisture contents. Good web formation is important in all grades of paper, more so in some grades than others. It is especially important in papers designated for printing, and, generally speaking, controlled web formation is more important in the lighter weight papers, e.g., carbon tissue and the like.

One means for achieving good web formation is by 3,391,057 Patented July 2, 1968 controlling the rate of water drainage from the Wet sheet. If the drainage is exceedingly rapid, pores of uneven thickness will form which will cause the final fiber product to have a spotty, non-uniform appearance. These spots in the sheet are undesirable esthetically, as well as rendering the fiber product unsuitable for high strength and other applications where uniformity is a requisite.

Rapid water removal from the web is, of course, desirable from the standpoint of economical speed of operation, but it is sometimes necessary to sacrifice speed to allow the fiber mat to form gently and more uniformly. Hence, a balance must be struck between a rapidly drained web and a uniformly laid one to obtain desirable paper products suitable for commercial acceptance.

Drainage rate of the liquid from the wet-laid web is dependent in large measure upon the degree of beating that the fibrous material has received. This beating fibrillates the fibers so that a network of fine fibrils is made available to interlock and hold the Web together. Thus, controlling the degree of heating or fibrillation of the fibers has been a principal means of controlling drainage rate, but again, a balance must be struck between the overall uniformity of the web, controlled principally by the drainage rate, and the degree of fibrillation of the fibers controlled principally by the degree of beating. It is generally observed in conventional paper-making from cellulose pulp that the difficulty encountered in web formation is that drainage rates are too slow for desirable machine speeds.

These features of paper and related structures manu-v factured from the traditional cei'iulosic fibrous materials have been quite well worked out and are not presently particularly burdensome. However, when non-cellulosic, synthetic polymeric fibrous products are employed to prepare paper-like and related webs thereof including nonwoven fabrics, felts, and film-like products, other difiiculties are encountered. For one thing, the non-cellulosic fibrous products are, for the most part, not readily or substantially fibrillatable so that good bond strength through this medium alone, i.e., fibrillation, is not generally attainable to an acceptable degree. Beating the fibers to induce fibrillation frequently merely break the fibers into shorter lengths without creating the desired level of fibrillation. This inability of the non-cellulosic fibers to fibrillate has been overcome in many instances by applying a binder to the Web to achieve the necessary fiber-to-fiber bonds. Without the aid of substantial fibrillation, controlling the rate of drainage from webs of the non-cellulosic fibers via controlled degree of fibrillation is not particularly effectual or useful. Moreover, it is generally observed that the rate of drainage from a web of non-cellulosic fibers is too fast resulting in nonuniform deposition of the fibers in the Wet web. This is contrary to the relatively slow rates observed when the conventional cellulosic fibers are employed.

From the foregoing, it can be appreciated that the difiiculties are accentuated when attempts are made to prepare paper-like or other non-woven fibrous products from non-beaten or nonfibrillated synthetic fiber materials. Here uniform web formation is exceedingly difficult to attain because drainage tends to be too rapid as well as unpredictable.

It would be a significant advantage and it is the chief object and primary concern of this invention to provide aqueous suspensions of synthetic polymeric fibrous materials from which a uniform wet-laid web can be deposited. It is a further object to provide a means for preparing these aqueous suspensions. It is a further object to provide a means for controlling the rate of drainage from a wetlaid web of these fibrous materials. It is a still further object to provide -a means for controlling the rate of drainage from a wet-laid web of these fibrous materials independently of the degree of fibrillation of the fibrous material. It is a yet further object to provide a means for preparing a uniform wet-laid web of these fibrous products.

These and additional objects and cognate benefits and features are obtained in and by practice of the invention which involves, briefly, preparing an aqueous suspension of fibrous material of at least about 50 weight percent of a non-cellulosic, synthetic polymeric substance containing a small amount of a water-soluble acrylamide polymer uniformly dispersed throughout the suspension, and then depositing a web of the fibrous material into a predetermined shape and thickness.

Fibrous material as used in the present specification and claims is intended to mean fiber-like material of any length that can be suitably cast into a web-like structure from an aqueous suspension. This includes relatively long and continuous lengths which are often referred to as continuous filaments as well as shorter cut lengths commonly referred to as staple. Ordinarily, staple of about A inch up to 23 inches long is employed in the present webforming suspensions.

The presence of the acrylamide polymer in the aqueous suspension apparently has a retarding influence on the rate of drainage of the aqueous liquid from the wet-laid web of noncellulosic fibrous material, whether it be unfibrillated, essentially unfib'rillated or highly fibrillated, as it is deposited upon the paper machine wire or similar web-forming device. While the notably significant changes in drainage rates are not so apparent when non-fibrillated fibrous materials are employed, nonetheless, significantly improved and totally acceptable uniformity of web formation results by practice of the present invention. The present method eminently enhances not only the uniformness of the resulting web but also the properties of the final product. The present invention thus provides the added advantage of being able to regulate and to attain web uniformity, for a given degree of fibrillation, and independently of the degree of fibrillation.

The acrylamide polymers utilized in the present invention are those of relatively high molecular weight, generally those having an average molecular weight in the neighborhood of at least about 750,000 and preferably at least about 1 million and including the ultra-high molecular weight acrylamide polymers described in U.S. 3,019,157. These polymers can be characterized by a viscosity of at least about 3 centipoises for a 0.5 weight percent solution of the acrylamide polymer in distilled water and adjusted to a pH of 3 to 3.5 at a temperature of 25 C., as determined with an Ostwald viscosimeter.

The term acrylamide polymer, as employed in the present specification and claims, is inclusive of the homopolymer of acrylamide and also copolymers of acrylamide with up to about 30-40 percent by weight of other suit-able monomers such as acrylic and methacrylic acid and their alkyl esters, methacrylamide, styrene, vinyl acetate, acrylonitrile, methacrylonitrile, vinyl alkyl ethers, vinyl and vinylidene chloride and the like, each such polymer being characterized by water solubility and viscosity properties as described above.

Water-soluble acrylamide polymers are sometimes characterized by a greater or less degree of hydrolysis, i.e., they may contain some free carboxyl groups. This condition is dependent upon the method of manufacture of the polymer, the presence or absence of small amounts of acrylic acid in the starting monomer and conditions of storage of the polymer. The polymer products appear to be equivalent whether the carboxyls result from copolymerization of acrylamide with acrylic acid or from hydrolysis of amide groups subsequent to polymerization. In the practice of the present invention, the operable acrylamide polymers encompass those generally having not more than about 3040 percent of the amide groups replaced by carboxyl groups, as set forth in the above definition of operable polyacrylamide products. The percentage of amide groups replaced by carboxyl groups in an acrylamide polymer is referred to hereinafter as the percent hydrolysis.

The effectiveness of the acrylamide polymer on slowing the rate of drainage is somewhat affected by the degree of hydrolysis and molecular weight of the polymer. That is, for a given suspension and a given amount of acrylamide polymer, slower drainage rates are usually obtained with acrylamide polymers having the higher degrees of hydrolysis and higher molecular weight.

In preparing the suspensions of the present invention it is desirable to add the acrylamide polymer as a dilute aqueous solution. This can be done prior to, during, or after the suspension of the fibrous material is formed in the aqueous dispersing medium. Preferably, when the suspension of fibrous material is beaten to promote fibrillation of the fibrous material if and when fibrillation is needed or desired, the acrylamide polymer is added after the beating operation. In any event, it is important that uniform mixing of the acrylamide polymer with the fibrous suspension be attained before the web is sheeted out from the suspension.

Only small amounts of the acrylamide polymer need be employed, and actually, any amount that serves to notably reduce the drainage rate, and more particularly that serves to notably improve the uniformity of a web cast from the suspension can be employed. Ordinarily, for apparent reasons, it is desirable to utilize as little of the acrylamide polymer as necessary to achieve the requisite uniformity in web structure. Generally, when fibrillated or beaten fibrous material is employed, an amount in the range of between about 0.01 and 3.0 weight percent, based on the dry weight of fibrous material in the suspension, is adequate in most instances, although larger amounts can be employed. On the other hand, when non-beaten or non-fibrillated fibrous material is employed, the amount of acrylamide polymer that is used is ordinarily in the range of about 0.1 to 10 weight percent and with some blends and materials up to about 20 or so weight percent, based on fibrous material dry weight. The nature and characteristic of the acrylamide polymer will bear upon the amount that is employed. As mentioned, molecular weight and degree of hydrolysis are factors that also have some influence on the drainage rate-controlling or uniform web-forming effectiveness of the acrylamide polymer. Additionally, the amount of acrylamide polymer employed will depend somewhat on the type and characteristics of non-cellulosic fibrous material and, as indicated, its condition, e.g., whether or not and to what degree it is fibrillated and the dispersability of the fibrous material in an aqueous medium. For instance, increasing the beating of the pulp (and in particular, the fibers) ordinarily will decrease the drainage rate, and additionally, increased beating increases the bursting and tensile strengths of the resulting paper, but causes a reduction in tear strength. Thus, it can be seen the properties desired in the final product will influence the degree of beating which in turn will influence the amount of acrylamide polymer required to achieve an adequate drainage rate to assure a uniform Web. The actual amount of acrylamide polymer that is required to achieve the desired drainage rate and web uniformity can be readily ascertained once the materials are specified either directly from the herein specific delineations or by running test runs with the desired materials following the precepts of the invention.

The pH of the aqueous suspension has an influence on the uniformity of the web formed from the acrylamide polymer-containing suspension or pulp. It is generally found that a pH of about 4 or lower results in non-uniform webs having thin and heavy areas. Preferably, a neutral pH is used. A pH higher than 7 can be employed but no particular enhancements in Web uniformity are noted over a pH of about 6-7.

As a rule, it is preferred in the practice of the present invention that coupling agents such as alum not be used because it is frequently observed that they counteract the drainage rate retarding effect of the acrylamide polymer and tend toward less uniform webs than when the acrylamide polymer alone is employed.

Any of the characteristically non-cellulosic, synthetic fibrous materials can be utilized in the preparation of suspensions and sheeting paper-like and non-woven products therefrom in accordance with the invention. Thus, by way of example, fibrous material can be used prepared from polymers of cellulose acetate; polyamides; e.g., polymerized epsilon-caprolactam, copolymerized hexamethylene diamine and adipic acid; polyesters, e.g., polyethyleneterephthalate; polyolefins, e.g., polyethylene and polypropylene. The acrylic fibers, i.e., those containing at least about 80 weight percent polymerized acrylonitrile in the polymer molecule, are particularly adapted and suited for use in the present invention. Typical vinyl monomers that may be polymerized with acrylonitrile in preparation of the acrylic fiber polymers include; vinyl pyridine, vinyl acetate, methyl acrylate, methyl methacrylate, sodium styrene sulfonate, etc. The fibers may be wet, dry, or melt spun prior to being dispersed or cut to staple lengths and dispersed as a pulp or suspension. In this connection, suspensions and webs can be made from fibers such as those water-fibrillated wet-spun acrylonitrile polymer fibers of US. 2,810,646, or, these same type of fibers that are still in an uncollapsed gel or aquagel state at the time of fibrillating and sheeting as discussed in US. 3,047,055. Additionally, suspensions of fibrids as discussed in US. 3,- 068,527 can be beneficially enhanced by the addition of the acrylamide polymers in the preparation of uniform weblike structures in accordance with the present invention.

Of course, blends of the above indicated non-cellulosic fibrous products can be employed. In addition, blends of the above indicated fibrous products with conventional cellulosic pulp or paper-making fibrous material, such as wood pulp and cotton linters, can be utilized. When these are employed, the blend should not contain more than about 50 and preferably not more than about 25 weight percent of the cellulosic material, based on the weight of the blend. When the cellulosic material is present in amounts greater than about 25 weight percent, the effectiveness of the acrylamide polymer tends to be diminished, although beneficial effects in uniform web formation are obtained until the amount of cellulosic material approaches about 50 weight percent.

The following examples further illustrate the invention wherein, unless otherwise specified, all parts and percentages are by weight.

Example 1 A fiber spinning solution was prepared from polyacrylonitrile homopolymer dissolved in an aqueous about 60 weight percent zinc chloride solution which was extruded into an aqueous coagulating bath to form a bundle or tow of filaments. The filaments were withdrawn from the bath and washed free of residual solvent and given an orientation stretch. The still wet, uncollapsed fibers were cut into A-inch staple lengths, two-gram portions of which were charged to a Waring Blendor set at low speed and beaten for 30 minutes. The slurry of gel was then diluted with water. An acrylamide polymer (about 70% acrylamide copolymerized with about 30% acrylic acid) was added as a dilute aqueous solution. Final dilution of slurry was to 5700 milliliters. The resulting fibrous suspension was then placed in the receiving well of a Williams handsheet mold (8" x 8" screen). A control sample was also prepared in which none of the acrylamide polymer was added to the slurry. The drain valve was opened to allow water to leave by gravity, leaving behind a wet, fibrous mat on the mold screen. The time elapsing between the opening of the drain valve and the moment air was first heard rushing through the mold screen (indicating that the majority of water has left the mold) was carefully observed and recorded as drain time. The results are set forth in Table I. Significant improvement in uniformity of the resulting sheet or web was noted in the sheets prepared from the 6 suspensions to which the acrylamide polymer had been added in contrast to the sheet from the control suspension. TABLE I Percent acrylamide polymer (based Drain time on dry fiber weight) added to slurry: (seconds) Example 2 A preboiled sample, i.e., boiled for 5 minutes in an aqueous bath of -inch gel fiber polyacrylonitrile staple prepared as described in Example 1 was formed into a sheet from the slurry or pulp, with drain time being measured by a Williams Precision Freeness Tester. Freeness is measured by the ease with which water passes through paper-making fibers while they are being formed into a wet mat on the perforated plate of the Freeness tester. Freeness is therefore a measure of the rate of drainage of water from the pulp, and is measured as the time taken for the complete drainage of stock of a definite consistency through a screen in the bottom of the tester. The preboiled sample was beaten for 12 minutes in the Waring Blendor before being sheeted out. The results of freencss measurement are set forth in Table II.

TABLE II Percent acrylamide polymer added to slurry (based on dry fiber weight):

Williams Precision Freeness (seconds) Example 3 A sample of 3 denier polyacrylonitrile textile fibers was cut to flt-inch staple length and beaten in a Waring Blendor for 15 minutes. About 0.25%, based on dry fiber weights, of an acrylamide polymer of about 70% acrylamide and 30% acrylic acid was added to the slurry and thoroughly mixed therein. A control was also run in which no acrylamide polymer was added to the slurry. The pH of the slurry was varied with HCl or NaOH and handsheets were cast from the solutions as before. The effect of the pH on drain time, as measured by Williams Freeness, is set forth in Table III.

TABLE III pH of slurry: Williams Freeness 1 (sec./ g. 6-7 (control) 1.5

Defined here as: (The time in seconds to drain 1 liter of an aqueous 0.1% fiber suspension) minus (the time in seconds to drain 1 liter of water) divided by the dry weight of fiber present in the suspension being tested.

Example 4 The procedure of Example 3 was repeated excepting that the fibers were not beaten and 2% of the acrylamide polymer was added to the slurry, based on fiber dry weight. Instead of determining drain time in this experiment, however, a formation number was obtained which is a direct measurement of the uniformity of the resulting web, i.e., after the web is dried. The formation number was determined by measuring the reflectance at numerous random locations over the web, and then determining the sum of the variations from the average reflectance value of the web. A thin area in the web gives a low reflectance reading and a thick area of the web gives a high reflectance reading (more light is reflected from the thick areas whereas the light passes through the thin areas). Intermediate thicknesses, of course, give intermediate reflectance. These values are recorded in Table IV. The lower the formation number the more uniform is the web.

TABLE IV TABLE VII pH of slurry: Formation number Percent Acrylamide 6-7 (COI1fI0 Polynlel Added to Time Gel Beaten Drain Time (seconds) 6 7 4 PulpbdJased (111m dry (minutes) 1' r 3 4 6O l 0 welg t) 0 15 2.0 9 10 40 0.5 2.9 Example 5 0 4.5 0.5 30 34.0 Tow sllnllar to that of Example 1 was cut into /LlllCll staple, beaten for minutes as in Example 1, and tested Example 8 in a similar manner. The pH of the pulp was adjusted to 10 7.5. Alum was added in some runs to illustrate its effect In this experiment several different kinds of synthetic on the efiicacy of the acrylamide polymer. The results polymer staple fibers, including blends thereof wlth paperare set forth in Table V. making wood pulp, were cast into sheets in accordance TABLE V with the invention. Handsheets that were formed were 1 Percent Acrylamide Percentmum 1.) made up of A inch staple length fibers or gel fibers, wlth Polymer Added to Added to Pulp (based Drain Time (seconds) the exception of the wood pulp fibers. The basis weight of p 25 dry on dfyfiber Wt) all handsheets was approximately 2 oz./yd. The aqueous fiber suspensions were agitated in a Waring Blendor for 8 5 8 one minute, after which the acrylamide polymer solution 0.5 1.0 19 20 was mixed in. Samples were removed from sheet mold Example 6 via a damp paper blotter or a 100-mesh screen. The webs from polyacrylonitrile (PVC) fibers were cold pressed fibers of Example 1 i h 1 Staple between felts, placed on a ZOO-mesh screen backed wlth i g 3 30 g Bllfindol paper blotter and chrome plate, topped with a chrome an 8 out as m xafnp cry 8 PO 5 plate, and dried at 315 F. for 30 seconds at 15 psi. The of "arymg degrees of hydlolysls were added to sampfes following required different drying procedures: 100%, thus pepared and a control Sample Q rflcrylamlde lS-denier nylon, 6- and 3-denier Dacron polyester dried polymer) was l The .efiect on drfnn of the at 300 p.s.i. for one minute at 315 F.; 8-denier rayon and various acrylamlde polymers ls set forth in Table VI. 3 deniel. Odom (acrylic) dried at 300 psi for 30 TABLE VI 30 onds at 315 F., and at 15 p.s.i. for 30 seconds; 4-denier l r eent A r er n de D T d D [H dr polypropylene dried at 300 psi. for 30 seconds; 4-denier o ynler e 0 rain ime sccon s e reeo y olysis 2 Pulp (based on dry b (percent) polypropylene dr ed at 300 psi. for 30 seconds at 270 fiber weight) F.; and 1% denier rayon (RD-101) dried at 15 p.s.1. 0 50 33 O m 05),) for two minutes at 235 F. The acrylarnide polymer 5 0.50 15.0 ca. 4-5 30 (70% acrylanllde, 30% acrylic acid) was added as an 8' 1,112 aqueous 0.3% solution in concentrations of 0, 2, 10 and 20%, based on weight of dry fiber in the slurry. Example 7 The formation number, determined as described in Ex- Gel fibers of Example 1 were cut into %-inch staple, ample 4, tensile strength, modulus, extension and tearing preboiled and beaten as in Example 1 for varying periods 40 strength, determined with an Instron tester, were ascerof time in a Waring Blendor, and tested in a similar mantained for each sheet formed. These results are set forth ner. The results are set forth in Table VII. in Table VIII.

TABLE VIII Weight Percent Type of Fiber ill Slurry and denier/fiber Acrylamide in Formation Tensile (lbs./in./ Tear (lbs./oz./yd. Modulus (lbs) Percent Ex (d/f) Slurry (based 011 Number oz./yd. tension fiber dry Weight) PVCN (gel (3 01/0 0 109 0 5 0.100 650 2 4 2 27 10 52 e. 0 0. 105 515 2. 7 20 6.6 0. 113 050 2. 7 PVCN fiber (3 (ill) 0 2%8 0. 25 0. 030 110 0. 00

2 1 10 55 0. 4s 0. 028 250 0. 5 20 2s 0. 72 0. 040 410 0. 5 Nylon (15 d/i) 0 188 10 50 20 4e Dacron (3 d/i) 0 218 10 150 20 Ol'lon (3 d/f) 0 107 10 102 20 30 Polypropylene (4 d/f) 10 275 0 7 20 105 75% PVCN gel (3 d/i) 0 43 25% wood pulp, blend 10 18 50% PVCN gel (3 d r). 0 23 50% wood pulp, blend.. 10 25 50% PVCN fiber (3 dd) 0 22 50% wood pulp, blend 10 17 50% Orloll (a d/f).... 0 35 50% wood pulp, blend. 10 18 50% nylon-6 (l5 d/f). 0 5 50% wood pulp, blend" 10 18 wood pulp 0 17 6. 8 0.135 1, 965 2. 3 10 22 5. 8 0.115 1, 220 2. 3 50% PVoN gel (3 d/r) 0 s7 1. 75 0. 207 4a 0. 0 50% PVCN tiller 3 am, ble 10 25 2. 45 0. 057 500 1. 2 50% PVCN gel (3 0/0.... 0 124 1. 3s 0.108 025 0. 0 50% Ollon (3 d/f). blen 10 25 2.38 0.10 550 1.0 50% PVCN gel (3 0/0.. 0 s2 1. 0 0. 073 so 2. 2 50% nylon6 (3 d/i), l)l0l 10 27 0.8 0. 00 25 2. 4 50% PVC-N u (3 0/0.. 0 30 3. 3 0.13 .0 1.2 50% rayon (1.5 tl/l'), blur l0 12 it. 5 0. I525 700 I g Example 9 Uncollapsed gel filaments were prepared according to the procedure of Example 1 excepting they were kept in continuous filament form and were not cut to staple length. A bundle of the continuous filament gel fibers was passed through a water trough and spread or dispersed in a water bath to which was added about 0.01 weight percent of the acrylamide polymer described in Example 1. It was observed that the bundle readily separated into individual filaments. The water-filament dispersion was collected on a revolving screen, giving a uniform web of continuous filaments which was dried to a uniform integral web of the continuous filaments.

When the foregoing was repeated except to eliminate the addition of acrylamide polymer, the resulting web was much less uniform than the web prepared from the dispersion containing the acrylamide polymer. Also, the bundle of filaments when added to the water remained substantially intact, with very little separation into individual filaments.

What is claimed is:

1. An aqueous suspension of (a) fibrous material, said fibrous material containing at least about 50 weight percent of a non-cellul-osic, synthetic polymer, and (-b) a water soluble acrylamide polymer having a molecular weight in excess of about 750,000 and a percent hydrolysis not in excess of about 40 percent in an amount of between about 0.01 and 20 weight percent based on fibrous material dry weight, said suspension having a pH not lower than about 4.

2. The suspension of claim 1, wherein said fibrous material is continuous filament fibrous material.

3. The suspension of claim 1, wherein said fibrous material is of a discontinuance staple length that has been fibrillated by a mechanical beating operation.

4. The suspension of claim 1, wherein said fibrous material is of a discontinuous staple length that has been fibrillated by a mechanical beating operation, and said suspension contains between about 0.01 and 3 weight percent of said acrylamide polymer, based on fibrous material dry weight.

5. An aqueous suspension of (a) fibrillated, papermaking length, wet-spun, uncollapsed gel fibers of an acrylonitrile polymer having at least about 80 weight percent polymerized acrylonitrile in the polymer molecule, and (b) from about 0.01 to about 3.0 weight percent, based on dry weight of said fibers, of a water soluble acrylamide polymer having a molecular weight in excess of about 750,000 and a percent hydrolysis not in excess of about 40 percent, said suspension havinga pH not lower than about 4.

6. A method for increasing the uniformity of a nonwoven web sheeted-out on a porous base from an aqueous suspension of staple length fibrous material, said fibrous material containing at least about 50 weight percent of a non-cellulosic, synthetic polymer, comprising, prior to sheeting out said non-woven web, mixing with said aqueous suspension of fibrous material a water-soluble acrylamide polymer having a molecular weight in excess of about 750,000 and a percent hydrolysis not in excess of about 40 percent in an amount of between about 0.01 and 20 weight percent based on fibrous material dry weight, said suspension having a pH not lower than about 4.

7. The method of claim 6, wherein said fibrous material is first fibrillated by being subjected to a mechanical beating operation before said acrylamide polymer is mixed with the aqueous suspension thereof.

8. The method of claim 6, wherein said fibrous material consists essentially of fibers of an acrylonitrile polymer having at least about weight percent polymerized acrylonitrile in the polymer molecule.

9. The method of claim 8, wherein said acrylonitrile polymer fibers are wet spun and in an uncollapsed gel condition.

10. The method of claim 6, wherein between about 0.01 and 3 weight percent of said acrylamide polymer, based on fibrous material dry weight, is mixed with said aqueous suspension of fibrous material, and said fi-brous material has been fibrillated by a mechanical beating operation.

11. A method for increasing the uniformity of a nonwoven web that is sheeted-out on a porous base from an aqueous suspension of wet spun, uncollapsed gel fibers of an acrylonitrile polymer having at least about 80 weight percent polymerized acrylonitrile in the polymer molecule, comprising, prior to sheeting out said non-woven web, mixing with said aqueous suspension of gel fibers from about 0.01 to about 3.0 weight percent, based on dry weight of said fibers, of a water soluble acrylamide polymer having a molecular weight in excess of about 750,000 and a percent hydrolysis not in excess of about 40 percent, said suspension having a pH not lower than about 4.

12. The method of claim 11, wherein said gel fibers are discontinuous staple length fibers.

References Cited 1 UNITED STATES PATENTS 3,052,595 9/1962 Pye 162l64 3,067,087 12/ 196-2 'Gorski et al. 162-157 3,255,072 6/1966 Sheetz l62--168 S. LEON BASHORE, Primary Examiner.

DONALL H. SYLVESTER, Examiner.

R. BAIEFSKY, Assistant Examiner. 

